Variable displacement vane pump

ABSTRACT

A variable displacement vane pump includes: a control orifice that imparts resistance to a flow of working oil discharged from pump chambers; a flow-amount control valve that operates in accordance with an upstream-downstream differential pressure of the control orifice and controls a flow amount of the working oil discharged from the pump chambers; a variable control valve that is operated by the working oil that has passed through the control orifice and controls an amount of eccentricity of a cam ring with respect to a rotor by controlling a pressure difference between a first fluid pressure chamber and a second fluid pressure chamber; and a return passage that is connected to the flow-amount control valve and circulates a part of the working oil discharged from the pump chambers through a suction passage.

TECHNICAL FIELD

The present invention relates to a variable displacement vane pump thatis used as a fluid pressure source in a fluid pressure apparatus.

BACKGROUND ART

As conventional variable displacement vane pumps, there are pumps inwhich a discharge capacity is changed by changing an amount ofeccentricity of a cam ring with respect to a rotor by making the camring swing about a pin as a support point.

JP2009-275537A discloses a variable displacement vane pump that includesa control valve that operates in accordance with an upstream-downstreamdifferential pressure of a flow-amount detection orifice and controls anamount of eccentricity of a cam ring with respect to a rotor, a returnpassage that returns, to a suction passage, a part of working fluid thathas been discharged from pump chambers through a discharge passage, anda flow dividing valve that adjusts an opening area of the return passageto the discharge passage.

With the variable displacement vane pump disclosed in JP2009-275537A,when the rotating speed of the rotor is increased and theupstream-downstream differential pressure of the flow-amount detectionorifice reaches a predetermined value, the amount of eccentricity of thecam ring is reduced by the control valve. Thereby, the dischargecapacity of the pump chambers is reduced, and the flow amount dischargedfrom the variable displacement vane pump is controlled so as to achievea predetermined flow amount.

SUMMARY OF INVENTION

With the variable displacement vane pump disclosed in JP2009-275537A,when the flow amount of the working fluid discharged from the pumpchambers reaches the flow amount at which a predeterminedupstream-downstream differential pressure of the flow-amount detectionorifice is generated, the flow amount of the working fluid is controlledto a constant flow amount by the control valve so as to maintain thedischarge flow amount. Thereby, the working fluid is guided to thereturn passage at the returning flow amount that is the differencebetween the discharge flow amount of the variable displacement vane pumpcontrolled by the control valve so as to be constant and the flow amountof the working fluid guided to the discharge passage by being controlledby the flow dividing valve. As described above, with the variabledisplacement vane pump disclosed in JP2009-275537A, while the dischargeflow amount is controlled by the control valve so as to be constant, thereturning flow amount is substantially constant.

With the variable displacement vane pump described above, because thedischarge flow amount is controlled by the control valve and thereturning flow amount becomes substantially constant, there is a risk inthat, when the rotating speed of the pump is high, cavitation may becaused due to insufficient suction.

An object of the present invention is to provide a variable displacementvane pump that is capable of suppressing occurrence of cavitation.

According to one aspect of the present invention, A variabledisplacement vane pump includes: a rotor linked to a driving shaft; aplurality of vanes provided so as to be able to reciprocate in a radialdirection relative to the rotor; a cam ring having an innercircumferential surface on which tip ends of the vanes slide by rotationof the rotor; pump chambers defined by the rotor, the cam ring, andpairs of the adjacent vanes; a suction passage configured to guideworking fluid to the pump chambers; a first fluid pressure chamber and asecond fluid pressure chamber defined in an outer-circumferentialaccommodating space on outer side of the cam ring, the first fluidpressure chamber and the second fluid pressure chamber being configuredto make the cam ring eccentric with respect to the rotor by pressuredifference between the first fluid pressure chamber and the second fluidpressure chamber; a control restrictor configured to impart resistanceto a flow of the working fluid discharged from the pump chambers; aflow-amount control valve operated in accordance with anupstream-downstream differential pressure of the control restrictor, theflow-amount control valve being configured to control flow amount of theworking fluid discharged from the pump chambers; a variable controlvalve operated by the working fluid that has passed through the controlrestrictor, the variable control valve being configured to control anamount of eccentricity of the cam ring with respect to the rotor bycontrolling pressure difference between the first fluid pressure chamberand the second fluid pressure chamber; and a return passage connected tothe flow-amount control valve, the return passage being configured tocirculate a part of the working fluid discharged from the pump chambersthrough the suction passage.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 is a hydraulic circuit diagram of a variable displacement vanepump according to an embodiment of the present invention.

FIG. 2A is a graph showing a flow amount characteristic of the variabledisplacement vane pump according to the embodiment of the presentinvention and is a diagram showing a case in which a flow amountrequired for operation of a variable control valve is less than acracking flow amount of a flow-amount control valve.

FIG. 2B is a graph showing the flow amount characteristic of thevariable displacement vane pump according to the embodiment of thepresent invention and is a diagram showing a case in which the flowamount required for operation of the variable control valve is greaterthan a maximum flow amount of the flow-amount control valve.

FIG. 2C is a graph showing the flow amount characteristic of thevariable displacement vane pump according to the embodiment of thepresent invention and is a diagram showing a case in which the flowamount required for operation of the variable control valve is greaterthan the cracking flow amount of the flow-amount control valve, but isless than the maximum flow amount of the flow-amount control valve.

FIG. 3 is a hydraulic circuit diagram of a variable displacement vanepump according to a comparative example of the present invention.

FIG. 4A is a graph showing a flow amount characteristic of the variabledisplacement vane pump according to the comparative example of thepresent invention and is a diagram showing a case in which the flowamount required for operation of the variable control valve is less thana flow amount controlled by a flow-amount control valve.

FIG. 4B is a graph showing the flow amount characteristic of thevariable displacement vane pump according to the comparative example ofthe present invention and is a diagram showing a case in which the flowamount required for operation of the variable control valve is greaterthan the flow amount controlled by the flow-amount control valve.

DESCRIPTION OF EMBODIMENTS

A variable displacement vane pump 100 according to an embodiment of thepresent invention will be described below with reference to thedrawings.

The variable displacement vane pump 100 (hereinafter, simply referred toas “vane pump ”) is used as a hydraulic source for a hydraulic apparatusmounted on a vehicle, such as, for example, a power steering apparatus,a transmission, and the like.

As shown in FIG. 1, the vane pump 100 includes a pump cartridge 101 thatdischarges working oil (working fluid), a flow-amount control valve 102that controls the flow amount of the working oil that is discharged fromthe pump cartridge 101 through a discharge passage 41 and supplied to ahydraulic apparatus 18, and a variable control valve 103 that controlsthe flow amount of the working oil that is discharged from the pumpcartridge 101.

In addition, the vane pump 100 further includes a control orifice 104that is provided in the discharge passage 41 and serves as a controlrestrictor for imparting resistance to a flow of the working oildischarged from the pump cartridge 101 and a variable orifice 105 thatserves as a variable restrictor for imparting resistance to a flow ofthe working oil that has passed through the control orifice 104.

In the pump cartridge 101, motive power from an engine (not shown) as amotive-power source is transmitted to an end portion of a driving shaft1, and a rotor 2 linked to the driving shaft 1 is rotated. The rotor 2is rotated in the clockwise direction in FIG. 1.

The pump cartridge 101 includes a plurality of vanes 3 that are providedso as to be able to reciprocate in the radial direction relative to therotor 2, a cam ring 4 having an inner circumferential surface on whichtip ends of the vanes 3 slide by rotation of the rotor 2, and an annularadapter ring 5 that is provided so as to surround the cam ring 4.

A plurality of pump chambers 6 are defined within the cam ring 4 by anouter circumferential surface of the rotor 2, the inner circumferentialsurface of the cam ring 4, and pairs of adjacent vanes 3.

In the pump cartridge 101, as the rotor 2 is rotated, the working oil issucked into the pump chambers 6 through a suction passage 40 from a tank17 in a suction region at which the volumes of the pump chambers 6 areexpanded, and the working oil is discharged from the pump chambers 6through the discharge passage 41 in a discharge region at which thevolumes of the pump chambers 6 are contracted.

A support pin 10 for supporting the cam ring 4 is provided on an innercircumferential surface of the adapter ring 5. The cam ring 4 swingsaround inside the adapter ring 5 about the support pin 10 as asupporting point, and thereby, the cam ring 4 is made eccentric withrespect to the center of the rotor 2. As described above, the supportpin 10 is the supporting point for the swinging of the cam ring 4.

At a position axisymmetric to the support pin 10 with respect to thedriving shaft 1 in the inner circumferential surface of the adapter ring5, a seal member 11, which is in sliding contact with an outercircumferential surface of the cam ring 4 when the cam ring 4 swingsaround, is fitted.

As described above, in a space between the outer circumferential surfaceof the cam ring 4 and the inner circumferential surface of the adapterring 5, which is an outer-circumferential accommodating space on theouter side of the cam ring 4, a first fluid pressure chamber 15 and asecond fluid pressure chamber 16 are defined by the support pin 10 andthe seal member 11.

A first fluid pressure passage 47 of the variable control valve 103,which will be described later, is connected to the first fluid pressurechamber 15, and the working oil is guided through the first fluidpressure passage 47. A second fluid pressure passage 48 of the variablecontrol valve 103, which will be described later, is connected to thesecond fluid pressure chamber 16. A part of the working oil that hasbeen discharged from the pump chambers 6 is guided to the second fluidpressure chamber 16 through a restricting passage 50 provided with anorifice 106.

The cam ring 4 swings around the support pin 10 by pressure differenceof the working oil between the first fluid pressure chamber 15 and thesecond fluid pressure chamber 16. As the cam ring 4 swings around thesupport pin 10, the amount of eccentricity of the cam ring 4 withrespect to the rotor 2 is changed, and the discharge capacity of thepump chambers 6 is changed. When the pressure in the first fluidpressure chamber 15 is greater than the pressure in the second fluidpressure chamber 16, the amount of eccentricity of the cam ring 4 withrespect to the rotor 2 is reduced, and the discharge capacity of thepump chambers 6 is reduced. In contrast, when the pressure in the secondfluid pressure chamber 16 is greater than the pressure in the firstfluid pressure chamber 15, the amount of eccentricity of the cam ring 4with respect to the rotor 2 is increased, and the discharge capacity ofthe pump chambers 6 is increased. As described above, in the vane pump100, by the pressure difference between the first fluid pressure chamber15 and the second fluid pressure chamber 16, the amount of eccentricityof the cam ring 4 with respect to the rotor 2 is changed, and thedischarge capacity of the pump chambers 6 is changed.

A return passage 42 that is in communication with the suction passage 40is connected to the flow-amount control valve 102. A part of the workingoil that has been discharged from the pump cartridge 101 is guided tothe suction passage 40 through the flow-amount control valve 102 and thereturn passage 42. The flow-amount control valve 102 has a first spool20 that moves in response to an upstream-downstream differentialpressure between upstream and downstream of the control orifice 104 thatimparts resistance to the flow of the working oil that has beendischarged from the pump chambers 6. The first spool 20 is inserted intoa first-spool accommodating portion 21 in a freely slidable manner. Thefirst spool 20 has a first land portion 20A and a second land portion20B that are in sliding contact with an inner circumference of thefirst-spool accommodating portion 21. A first circular groove 20C thatopens to an outer circumferential surface of the first spool 20 isformed between the first land portion 20A and the second land portion20B.

A first pressure chamber 22 is defined between the first land portion20A of the first spool 20 and the one end portion of the first-spoolaccommodating portion 21. A second pressure chamber 23 is definedbetween the second land portion 20B of the first spool 20 and the otherend portion of the first-spool accommodating portion 21. A first controlpassage 43 that is in communication with the discharge passage 41 at theupstream side of the control orifice 104 is connected to the firstpressure chamber 22, and the working oil is guided to the first pressurechamber 22 from the upstream side of the control orifice 104. A secondcontrol passage 44 that is in communication with the discharge passage41 at the downstream side of the control orifice 104 is connected to thesecond pressure chamber 23, and the working oil that has passed throughthe control orifice 104 is guided from the downstream side thereof tothe second pressure chamber 23. As described above, while the workingoil that has been discharged from the pump chambers 6 is guided directlyto the first pressure chamber 22, the working oil that has beendepressurized by passing through the control orifice 104 is guided tothe second pressure chamber 23.

In the second pressure chamber 23, a first spring 24 serving as abiasing member for biasing the first spool 20 in the direction in whichthe volume of the second pressure chamber 23 is increased isaccommodated. Therefore, the first spool 20 is located at a positionwhere the load based on the upstream-downstream differential pressure ofthe control orifice 104 and the biasing force exerted by the firstspring 24 are balanced.

A return port 25 that guides the working oil from the first pressurechamber 22 to the return passage 42 is provided on the first-spoolaccommodating portion 21. In a state in which the upstream-downstreamdifferential pressure of the control orifice 104 is small and the firstspring 24 is extended, as shown in FIG. 1, the return port 25 is in astate closed by the first land portion 20A of the first spool 20. As theupstream-downstream differential pressure of the control orifice 104 isincreased and the first spool 20 moves against the biasing force exertedby the first spring 24, the return port 25 is opened.

On the inner circumference of the first-spool accommodating portion 21,a recessed opposing port 26 is formed at a position opposite to thereturn port 25, in other words, at a position symmetrical to the returnport 25 with respect to the axis of the first-spool accommodatingportion 21. The working oil that has flown into the opposing port 26from the first pressure chamber 22 is guided to the return port 25through the first circular groove 20C. By providing the opposing port 26on the first-spool accommodating portion 21, the pressure balance actingon the first spool 20 is improved, and the sliding property of the firstspool 20 against the first-spool accommodating portion 21 is improved.

When the rotation speed of an engine, in other words, the pump rotationspeed that is the rotation speed of the rotor 2 is low, theupstream-downstream differential pressure of the control orifice 104 issmall, and the state in which the return port 25 is closed is achieved.Thus, the working oil is not guided to the return passage 42.

As the pump rotation speed is increased, the upstream-downstreamdifferential pressure of the control orifice 104 reaches a predeterminedvalue at which the first spool 20 of the flow-amount control valve 102moves against the biasing force exerted by the first spring 24 and thereturn port 25 is opened. When the upstream-downstream differentialpressure of the control orifice 104 reaches the predetermined value atwhich the return port 25 is opened, in accordance with an opening areaof the return port 25, a part of the working oil that has beendischarged from the pump cartridge 101 is guided to the suction passage40 through the first pressure chamber 22, the return port 25, and thereturn passage 42. By operation of the flow-amount control valve 102 asdescribed above, a part of the working oil discharged from the pumpcartridge 101 is guided to the return passage 42, and the flow amount ofthe working oil guided to the hydraulic apparatus 18 is controlled so asto achieve a predetermined flow amount. In addition, resistance isimparted to the flow of the working oil passing through the return port25 in accordance with the opening area of the return port 25. Thus,flowing speed of the working oil guided to the return passage 42 isincreased, negative pressure is caused in the return passage 42. Becausenegative pressure is caused in this way, the working oil is sucked fromthe tank 17 more effectively, and the working oil can be supercharged toa suction port through the suction passage 40 more effectively.Therefore, occurrence of cavitation in the pump chambers 6 issuppressed.

The variable orifice 105 is provided at the downstream side of thecontrol orifice 104 in the discharge passage 41. More specifically, thevariable orifice 105 is provided on the discharge passage 41 at thedownstream side of a location at which the second control passage 44that is connected to the second pressure chamber 23 of the flow-amountcontrol valve 102 communicates with the discharge passage 41. Byproviding the variable orifice 105 as described above, the working oilto which resistance has been imparted by the variable orifice 105 isprevented from being guided to the second pressure chamber 23 of theflow-amount control valve 102. The variable orifice 105 is a variablerestrictor capable of changing resistance to be imparted to the flow ofthe working oil passing therethrough by changing its opening area bycontrolling amount of current flowing to a solenoid (not shown).

The variable control valve 103 has a second spool 30 that moves inresponse to the upstream-downstream differential pressure betweenupstream and downstream of the variable orifice 105 that is generated byguiding, to the variable orifice 105, the working oil that has passedthrough the control orifice 104. The second spool 30 has a third landportion 30A and a fourth land portion 30B that are in sliding contactwith an inner circumference of a second spool accommodating portion 31.A second circular groove 30C that opens to an outer circumferentialsurface of the second spool 30 is formed between the third land portion30A and the fourth land portion 30B.

A third pressure chamber 32 is defined between the third land portion30A of the second spool 30 and the one end portion of the second spoolaccommodating portion 31. A fourth pressure chamber 33 is definedbetween the fourth land portion 30B of the second spool 30 and the otherend portion of the second spool accommodating portion 31. A thirdcontrol passage 45 that is in communication with the discharge passage41 at a location between the control orifice 104 and the variableorifice 105 is connected to the third pressure chamber 32, and theworking oil is guided to the third pressure chamber 32 from the upstreamside of the variable orifice 105. A fourth control passage 46 that is incommunication with the discharge passage 41 at the downstream side ofthe variable orifice 105 is connected to the fourth pressure chamber 33,and the working oil is guided to the fourth pressure chamber 33 from thedownstream side of the variable orifice 105. As described above, whilethe working oil that has been discharged from the pump chambers 6 anddepressurized by the control orifice 104 is guided to the third pressurechamber 32, the working oil that has been depressurized by passingthrough the control orifice 104 and the variable orifice 105 is guidedto the fourth pressure chamber 33.

In the fourth pressure chamber 33, a second spring 34 serving as abiasing member for biasing the second spool 30 in the direction in whichthe volume of the fourth pressure chamber 33 is increased isaccommodated. Therefore, the second spool 30 is located at a positionwhere the load based on the upstream-downstream differential pressure ofthe variable orifice 105 and the biasing force exerted by the secondspring 34 are balanced.

The first fluid pressure passage 47 and the second fluid pressurepassage 48 that are in communication with the first fluid pressurechamber 15 and the second fluid pressure chamber 16, respectively, and adrain passage 49 that is in communication with the second circulargroove 30C and the suction passage 40 are connected to the second spoolaccommodating portion 31.

When the pump rotation speed is low, because the upstream-downstreamdifferential pressure of the variable orifice 105 is small, the secondspring 34 is extended, and thereby, the first fluid pressure passage 47is communicated with the second circular groove 30C and the second fluidpressure passage 48 is closed by the fourth land portion 30B of thesecond spool 30. In other words, the first fluid pressure chamber 15 iscommunicated with the drain passage 49 through the second circulargroove 30C, and the communication between the second fluid pressurechamber 16 and the second circular groove 30C is closed. The working oilthat has been discharged from the pump cartridge 101 is constantlyguided to the second fluid pressure chamber 16 through the restrictingpassage 50. With such a configuration, as shown in FIG. 1, the cam ring4 is brought into contact with the inner circumferential surface of theadapter ring 5 by the pressure in the second fluid pressure chamber 16,and thereby, the amount of eccentricity of the cam ring 4 with respectto the rotor 2 is maximized.

As the pump rotation speed is increased and the upstream-downstreamdifferential pressure of the variable orifice 105 is increased, thesecond spool 30 moves against the biasing force exerted by the secondspring 34, and thereby the third pressure chamber 32 is communicatedwith the first fluid pressure passage 47 and the second circular groove30C is communicated with the second fluid pressure passage 48.

As the pump rotation speed is increased further, the opening area of thefirst fluid pressure passage 47 to the third pressure chamber 32 isincreased, and the opening area of the second fluid pressure passage 48to the second circular groove 30C is increased. The working oil in thethird pressure chamber 32 is supplied to the first fluid pressurechamber 15 through the first fluid pressure passage 47, and the workingoil in the second fluid pressure chamber 16 is discharged to the tank 17through the second fluid pressure passage 48, the second circular groove30C, and the drain passage 49. With such a configuration, the cam ring 4moves such that the amount of eccentricity with respect to the rotor 2is reduced in response to the pressure difference between the firstfluid pressure chamber 15 and the second fluid pressure chamber 16.

As the pressure difference between the first fluid pressure chamber 15and the second fluid pressure chamber 16 is increased in response to theincrease in the pump rotation speed, the cam ring 4 is brought intocontact with the inner circumferential surface of the adapter ring 5 andthe amount of eccentricity of the cam ring 4 is minimized, and thereby,the discharge capacity of the pump chambers 6 becomes a minimumdischarge capacity. As described above, because the variable controlvalve 103 is operated in accordance with the upstream-downstreamdifferential pressure of the variable orifice 105, even when the pumprotation speed is increased, the discharge flow amount of the pumpcartridge 101 is controlled so as to be substantially constant.

The upstream-downstream differential pressure of the variable orifice105 is generated at amount in accordance with the opening area of thevariable orifice 105 that is controlled by the amount of current flow tothe solenoid and the passing flow amount passing through the variableorifice 105. Therefore, by controlling the opening area of the variableorifice 105 by the solenoid, it is possible to arbitrarily set thepassing flow amount of the variable orifice 105 that generates theupstream-downstream differential pressure for operating the variablecontrol valve 103.

Next, operation of the vane pump 100 will be described with reference toFIGS. 2 to 4. FIG. 2 is a graph showing the relationship between thepump rotation speed and the flow amount of the working oil of the vanepump 100. FIG. 3 is a hydraulic circuit diagram of a vane pump 200 as acomparative example, FIG. 4 is a graph showing the relationship betweenthe pump rotation speed and the flow amount of the working oil of thevane pump 200. In FIGS. 2 and 4, a flow amount Q shown with a solid lineis a supply flow amount of the working oil supplied to the hydraulicapparatus 18, and a flow amount Q1 shown with a broken line is adischarge flow amount of the working oil discharged from the pumpcartridge 101. In addition, in FIGS. 2 and 4, a flow amount Q2 shownwith a one-dot chain line is a flow amount of the working oil controlledby the flow-amount control valve 102. In addition, in FIGS. 2 and 4, aflow amount Q3 is a passing flow amount of the variable orifice 105required to generate the upstream-downstream differential pressure foroperating the variable control valve 103.

In the following description, the passing flow amount of the controlorifice 104 required to generate the upstream-downstream differentialpressure for operating the flow-amount control valve 102 is referred toas “the cracking flow amount”, the flow amount Q2 of the working oilcontrolled by the flow-amount control valve 102 is referred to as “thecontrol flow amount Q2”, and the control flow amount of the flow-amountcontrol valve 102 at the pump maximum rotation speed N1 used with thevane pump 100 is referred to as “the maximum control flow amount”. Inaddition, the passing flow amount Q3 of the variable orifice 105required to generate the upstream-downstream differential pressure foroperating the variable control valve 103 is referred to as “thevariable-control-setting flow amount Q3”, and the discharge flow amountof the pump cartridge 101 that is kept constant by the variable controlvalve 103 is referred to as “the constant discharge flow amount”.

The variable-control-setting flow amount Q3 is set by controlling theopening area of the variable orifice 105 by changing the amount ofcurrent flow to the solenoid. For example, in a case where the openingarea of the variable orifice 105 is set, by flow of the working oilpassing through the variable orifice 105 at the flow amount greater thanthe cracking flow amount, such that the upstream-downstream differentialpressure for operating the variable control valve 103 is generated, thevariable-control-setting flow amount Q3 becomes greater than thecracking flow amount of the flow-amount control valve 102.

In addition, in a case where the opening area of the variable orifice105 is set, by flow of the working oil passing through the variableorifice 105 at the flow amount smaller than the cracking flow amount,such that the upstream-downstream differential pressure for operatingthe variable control valve 103 is generated, thevariable-control-setting flow amount Q3 becomes smaller than thecracking flow amount of the flow-amount control valve 102.

For ease of understanding the vane pump 100, the vane pump 200 as acomparative example will be described with reference to FIGS. 3 and 4.

As shown in FIG. 3, the vane pump 200 includes the variable controlvalve 103 that is operated by the upstream-downstream differentialpressure of the variable orifice 105 provided on the discharge passage41 and the flow-amount control valve 102 that is operated by theupstream-downstream differential pressure of the control orifice 104provided on the discharge passage 41 at the downstream side of thevariable orifice 105. In other words, in the vane pump 200, theflow-amount control valve 102 is provided at the downstream side of thevariable control valve 103.

FIG. 4(a) is a diagram showing the relationship between the pumprotation speed and the flow amount in a case where thevariable-control-setting flow amount Q3 is set so as to be smaller thanthe cracking flow amount of the flow-amount control valve 102. FIG. 4(b)is a diagram showing the relationship between the pump rotation speedand the flow amount in a case where the variable-control-setting flowamount Q3 is set so as to be greater than the maximum control flowamount of the flow-amount control valve 102.

With the vane pump 200, as shown in FIG. 4(a), in a case where thevariable-control-setting flow amount Q3 is set so as to be smaller thanthe cracking flow amount of the flow-amount control valve 102, thedischarge flow amount of the working oil from the pump cartridge 101reaches the variable-control-setting flow amount Q3 in response to theincrease in the pump rotation speed, and thereby, the variable controlvalve 103 is operated. In other words, as the pump rotation speed isincreased, before the upstream-downstream differential pressure of thecontrol orifice 104 reaches a predetermined differential pressure atwhich the flow-amount control valve 102 is operated, theupstream-downstream differential pressure of the variable orifice 105reaches a predetermined differential pressure at which the variablecontrol valve 103 is operated, and thereby, the variable control valve103 is operated. Thus, the discharge flow amount from the pump cartridge101 is controlled to be constant so as to keep the discharge flowamount. In other words, as shown in FIG. 4(a), with the vane pump 200,when the upstream-downstream differential pressure of the variableorifice 105 reaches a predetermined value, the flow amount dischargedfrom the pump cartridge 101 is controlled as the constant discharge flowamount so as to keep the variable-control-setting flow amount Q3.

As described above, when the variable control valve 103 is operated,because the discharge flow amount from the pump cartridge 101 is notincreased even when the pump rotation speed is increased, the dischargeflow amount does not reach the cracking flow amount of the flow-amountcontrol valve 102. In other words, even in a case where thevariable-control-setting flow amount Q3 that is set so as to be smallerthan the cracking flow amount of the flow-amount control valve 102passes through the control orifice 104, the upstream-downstreamdifferential pressure for operating the flow-amount control valve 102 isnot generated at the control orifice 104. Thus, as shown in FIG. 4(a),the flow amount of the working oil that has passed through the variableorifice 105 is not controlled by the flow-amount control valve 102, andthe working oil whose flow amount is controlled by the variable controlvalve 103 so as to achieve the variable-control-setting flow amount Q3is guided to the hydraulic apparatus 18. As described above, in a casewhere the variable-control-setting flow amount Q3 is set so as to besmaller than the cracking flow amount of the flow-amount control valve102, because the flow-amount control valve 102 is not operated, theworking oil is not guided to the suction passage 40 through the returnpassage 42.

As shown in FIG. 4(b), in a case where the variable-control-setting flowamount Q3 is set so as to be higher than the maximum control flow amountof the flow-amount control valve 102, the discharge flow amount from thepump cartridge 101 is increased in response to the increase in the pumprotation speed and reaches the cracking flow amount of the flow-amountcontrol valve 102. Thus, the upstream-downstream differential pressureof the control orifice 104 reaches a predetermined value and theflow-amount control valve 102 is operated, and thereby, the return port25 is opened. The flow amount of the working oil that has beendischarged from the pump cartridge 101 is controlled by the flow-amountcontrol valve 102 so as to achieve the control flow amount Q2 and theworking oil is guided to the hydraulic apparatus 18. In this case,because the variable control valve 103 is in a non-operating state, thecam ring 4 is in the maximum eccentric state and the discharge capacityof the pump chambers 6 is maintained in the maximum state. Therefore, asthe pump rotation speed is further increased, the discharge flow amountfrom the pump cartridge 101 is increased in a manner proportional to theincrease in the pump rotation speed. When the discharge flow amount fromthe pump cartridge 101 is increased and reaches thevariable-control-setting flow amount Q3, the upstream-downstreamdifferential pressure of the variable orifice 105 reaches apredetermined value. Thereby, the variable control valve 103 isoperated, and as shown in FIG. 4(b), the discharge flow amount from thepump cartridge 101 is controlled so as to achieve thevariable-control-setting flow amount Q3 as the constant discharge flowamount.

As described above, with the vane pump 200, because the variable controlvalve 103 is provided at the upstream side of the flow-amount controlvalve 102, as the pump rotation speed is increased, the discharge flowamount from the pump cartridge 101 is controlled by the variable controlvalve 103 so as to achieve the variable-control-setting flow amount Q3,and so, the discharge flow amount does not exceeds thevariable-control-setting flow amount Q3. Therefore, a part of theworking oil guided to the flow-amount control valve 102 at thevariable-control-setting flow amount Q3 is guided to the suction passage40 as the returning flow amount. In other words, in the vane pump 200,as shown in FIG. 4(b), the returning flow amount guided to the returnpassage 42 is a difference between the control flow amount Q2 and thevariable-control-setting flow amount Q3 as the constant discharge flowamount.

In contrast, in the vane pump 100, as shown in FIG. 2(a), in a casewhere the variable-control-setting flow amount Q3 is set so as to besmaller than the cracking flow amount of the flow-amount control valve102 by controlling the amount of current flow to the solenoid, similarlyto the vane pump 200, the flow-amount control valve 102 is not operatedand the working oil is not guided to the suction passage 40 through thereturn passage 42. In this case, all of the working oil discharged fromthe pump cartridge 101 is guided to the hydraulic apparatus 18.

As shown in FIG. 2(b), in a case where the variable-control-setting flowamount Q3 is set so as to be greater than the maximum control flowamount of the flow-amount control valve 102, similarly to the vane pump200, the discharge flow amount from the pump cartridge 101 of the vanepump 100 is increased in response to the increase in the pump rotationspeed and reaches the cracking flow amount of the flow-amount controlvalve 102. Thereby, the working oil whose flow amount is controlled bythe flow-amount control valve 102 so as to achieve the control flowamount Q2 is guide to the hydraulic apparatus 18. In addition, a part ofthe working oil discharged from the pump cartridge 101 through thereturn passage 42 is guided to the suction passage 40.

As described above, in a case where the variable-control-setting flowamount Q3 is set so as to be greater than the maximum control flowamount of the flow-amount control valve 102, because the control flowamount Q2 does not reach the variable-control-setting flow amount Q3even when the pump rotation speed is increased, the variable controlvalve 103 is not operated and the cam ring 4 of the pump cartridge 101is maintained in the maximum eccentric state. Therefore, the dischargecapacity of the pump chambers 6 is maintained in the maximum state, andthe discharge flow amount from the pump cartridge 101 is increased in amanner proportional to the increase in the pump rotation speed.Therefore, as shown in FIG. 2(b), the difference between the dischargeflow amount Q1 of the pump cartridge 101, in which the dischargecapacity of the pump chambers 6 is in the maximum state (the cam ring 4is in the maximum eccentric state), and the control flow amount Q2 canbe used as the returning flow amount.

FIG. 2(c) is a diagram showing a case in which thevariable-control-setting flow amount Q3 is set between the cracking flowamount of the flow-amount control valve 102 and the maximum control flowamount. In this case, until the control flow amount Q2 reaches thevariable-control-setting flow amount Q3, the difference between thedischarge flow amount Q1 of the pump cartridge 101, in which thedischarge capacity of the pump chambers 6 is in the maximum state, andthe control flow amount Q2 is guided to the suction passage 40 as thereturning flow amount.

As the pump rotation speed is increased, the control flow amount Q2reaches the variable-control-setting flow amount Q3, and theupstream-downstream differential pressure of the variable orifice 105reaches a predetermined value, the variable control valve 103 isoperated. Thereby, as shown in FIG. 2(c), even when the pump rotationspeed is increased, the discharge flow amount from the pump cartridge101 is controlled so as to achieve the constant discharge flow amount atwhich the discharge flow amount becomes constant. Therefore, the workingoil is guided to the hydraulic apparatus 18 at thevariable-control-setting flow amount Q3, and the difference between thedischarge flow amount Q1 as the constant discharge flow amount and thevariable-control-setting flow amount Q3 is guided to the return passage42 as the returning flow amount.

As described above, with the vane pump 100, because the variable controlvalve 103 is operated by the working oil whose flow amount is controlledby the flow-amount control valve 102 so as to achieve the control flowamount Q2, the variable control valve 103 is not operated until thecontrol flow amount Q2 reaches the variable-control-setting flow amountQ3, and the amount of eccentricity of the cam ring 4 is maintained inthe maximum state. In other words, the discharge capacity of the pumpchambers 6 is maintained at the maximum discharge capacity. Thereby,with the vane pump 100, the working oil can be discharged from the pumpcartridge 101 at the flow amount equal to or greater than thevariable-control-setting flow amount Q3 in response to the increase inthe pump rotation speed, and the difference between the discharge flowamount Q1 and the control flow amount Q2 can be guided to the suctionpassage 40 as the returning flow amount. Therefore, with the vane pump100, it is possible to secure greater returning flow amount.

The variable-control-setting flow amount Q3 is set on the basis of, forexample, the pump rotation speed.

The setting shown in FIG. 2(a), in which the variable-control-settingflow amount Q3 is set so as to be smaller than the cracking flow amountof the flow-amount control valve 102, is used when the pump rotationspeed is low, for example. By reducing the discharge flow amount fromthe pump cartridge 101, torque of the vane pump 100 is reduced, and itis possible to improve a fuel consumption efficiency of a vehicle.

The setting shown in FIG. 2(b), in which the variable-control-settingflow amount Q3 is set so as to be greater than the maximum control flowamount of the flow-amount control valve 102, is used when the pumprotation speed is high, for example. By setting thevariable-control-setting flow amount Q3 so as to be greater than themaximum control flow amount of the flow-amount control valve 102, it ispossible to secure greater returning flow amount, and so, occurrence ofthe cavitation can be suppressed when the pump rotation speed is high.

When the flow amount guided to the hydraulic apparatus 18 reaches therequired flow amount in response to the increase in the pump rotationspeed, as shown in FIG. 2(c), the variable-control-setting flow amountQ3 may be set between the maximum control flow amount of the flow-amountcontrol valve 102 and the cracking flow amount. By setting thevariable-control-setting flow amount Q3 as described above, it ispossible to secure greater returning flow amount while supplying aconstant flow amount to the hydraulic apparatus 18. Thereby, occurrenceof the cavitation is suppressed when the pump rotation speed is high,and it is possible to prevent loss of energy caused by guiding theworking oil to the hydraulic apparatus 18 at the flow amount exceedingthe required amount and to improve the fuel consumption efficiency.

The settings of the variable-control-setting flow amount Q3 are notlimited to those based on the pump rotation speed, and the setting maybe performed on the basis of a driving state of a vehicle, an operatingstate of the hydraulic apparatus 18, and so forth. For example, evenwhen the pump rotation speed is low, when a gear of a vehicle isshifted, the vane pump 100 may be operated so as to output large torqueby setting the variable-control-setting flow amount Q3 so as to be equalto or greater than the maximum control flow amount of the flow-amountcontrol valve 102 and by maintaining the cam ring 4 in the maximumeccentric state.

According to the embodiment mentioned above, the advantages describedbelow are afforded.

According to the vane pump 100, a part of the working oil dischargedfrom the pump chambers 6 of the pump cartridge 101 is guided to thereturn passage 42 by the flow-amount control valve 102, and the flowamount of the working oil is controlled so as to achieve the controlflow amount Q2. Thereby, the variable control valve 103 is operated bythe working oil whose control flow amount is controlled by theflow-amount control valve 102. When the pump rotation speed is low andthe control flow amount Q2 is smaller than the variable-control-settingflow amount Q3, the variable control valve 103 is not operated and thedischarge capacity of the pump chambers 6 is maintained in the maximumstate. As described above, because the variable control valve 103 isoperated by the working fluid whose flow amount is controlled by thecontrol flow amount Q2, it is possible to discharge the working fluidfrom the pump chambers 6 of the pump cartridge 101 at the flow amountequal to or greater than the variable-control-setting flow amount Q3.Therefore, the difference between the discharge flow amount from thepump chambers 6 that is increased to the variable-control-setting flowamount Q3 or more in response to the increase in the pump rotation speedand the control flow amount Q2 is guided to the return passage 42.Therefore, it is possible to circulate greater amount of the working oilthrough the return passage 42 and to suppress occurrence of thecavitation.

In addition, by performing the setting such that the upstream-downstreamdifferential pressure for operating the variable control valve 103 isgenerated by passing the working fluid through the variable orifice 105of the vane pump 100 at the flow amount greater than the cracking flowamount, in other words, by setting the variable-control-setting flowamount Q3 so as to be greater than the cracking flow amount of theflow-amount control valve 102, it is possible to operate the flow-amountcontrol valve 102 before the variable control valve 103 in response tothe increase in the discharge flow amount Q1 of the pump cartridge 101due to the increase in the pump rotation speed. Thereby, it is possibleto operate the variable control valve 103 with the working fluid whoseflow amount is controlled so as to achieve the control flow amount Q2.Therefore, it is possible to secure greater returning flow amount bydischarging the working fluid from the pump chambers 6 of the pumpcartridge 101 at the flow amount equal to or greater than thevariable-control-setting flow amount Q3, and to prevent occurrence ofthe cavitation.

Embodiments of this invention were described above, but the aboveembodiments are merely examples of applications of this invention, andthe technical scope of this invention is not limited to the specificconstitutions of the above embodiments.

In the above-mentioned embodiment, the amount of eccentricity of the camring 4 with respect to the rotor 2 is controlled by the pressuredifference between the pressure of the working oil guided to the firstfluid pressure chamber 15 and the pressure of the working oil guided tothe second fluid pressure chamber 16. In contrast, it may be possible toprovide a biasing member (for example, a coil spring) that biases thecam ring 4 in the direction in which the amount of eccentricity isincreased. In this case, the amount of eccentricity of the cam ring 4 iscontrolled by the biasing force exerted by the biasing member and thepressure difference between the first fluid pressure chamber 15 and thesecond fluid pressure chamber 16.

This application claims priority based on Japanese Patent ApplicationNo. 2015-90303 filed with the Japan Patent Office on Apr. 27, 2015, theentire contents of which are incorporated into this specification.

1. A variable displacement vane pump comprising: a rotor linked to adriving shaft; a plurality of vanes provided so as to be able toreciprocate in a radial direction relative to the rotor; a cam ringhaving an inner circumferential surface on which tip ends of the vanesslide by rotation of the rotor; pump chambers defined by the rotor, thecam ring, and pairs of the adjacent vanes; a suction passage configuredto guide working fluid to the pump chambers; a first fluid pressurechamber and a second fluid pressure chamber defined in anouter-circumferential accommodating space on outer side of the cam ring,the first fluid pressure chamber and the second fluid pressure chamberbeing configured to make the cam ring eccentric with respect to therotor by pressure difference between the first fluid pressure chamberand the second fluid pressure chamber; a control restrictor configuredto impart resistance to a flow of the working fluid discharged from thepump chambers; a flow-amount control valve operated in accordance withan upstream-downstream differential pressure of the control restrictor,the flow-amount control valve being configured to control flow amount ofthe working fluid discharged from the pump chambers; a variable controlvalve operated by the working fluid that has passed through the controlrestrictor, the variable control valve being configured to control anamount of eccentricity of the cam ring with respect to the rotor bycontrolling pressure difference between the first fluid pressure chamberand the second fluid pressure chamber; and a return passage connected tothe flow-amount control valve, the return passage being configured tocirculate a part of the working fluid discharged from the pump chambersthrough the suction passage.
 2. The variable displacement vane pumpaccording to claim 1, further comprising a variable restrictor capableof changing resistance imparted to a flow of the working fluid that haspassed through the control restrictor, wherein the variable controlvalve is operated in accordance with the upstream-downstreamdifferential pressure of the variable restrictor.
 3. The variabledisplacement vane pump according to claim 2, wherein an opening area ofthe variable restrictor is set such that the upstream-downstreamdifferential pressure for operating the variable control valve isgenerated by allowing the working fluid to pass through the variablerestrictor at a flow amount that is greater than a passing flow amountof the control restrictor for generating the upstream-downstreamdifferential pressure for operating the flow-amount control valve.